Once you have installed SQL Server 2012, please do the following:
- Open up SQL Server Management Studio 2012
- Connect to the database server
- Expand the Security > Logins tab
- Locate the NTAUTHORITY\SYSTEM login
- Right-click on it and choose Properties
- On the page that appears, click on the "server roles" tab
- Check the box next to "sysadmin"
- Click OK
- Close SQL Management Studio
You should now be able to install Spira v3.x onto the server.